From: Josef 'Jupp' Schugt <jupp@...>
Date: 2002-10-27T01:46:59+09:00
Subject: Validating ISBN: Regex question

Hi!

I'm using  the following method to validate an ISBN, remove any ' '
or '-' from it and and change 'x' to 'X'.

|def validate_isbn!
|  match = /(\d)[- ]?(\d)[- ]?(\d)[- ]?(\d)[- ]?(\d)[- ]?(\d)[- ]?(\d)[- ]?(\d)[- ]?(\d)[- ]?([0-9xX])/.match(@isbn)
|  if match == nil
|    return 'ISBN pattern mismatch'
|  end
|  checksum = 0
|  @isbn = ''
|  for i in 1..10
|    case match[i]
|      when 'X', 'x'
|        checksum += 10
|        @isbn += 'X'
|      else
|        checksum += (11 - i) * match[i].to_i
|        @isbn += match[i]
|    end
|  end
|  (checksum.remainder(11) == 0 ? '' : 'in') + 'valid checksum'
|end

I'm not to happy about the lenghty regex but I don't see how to make
it shorter because using

| match = /(\d[- ]?){9,9}([0-9xX])/.match(@isbn)

is not possible - it does not split the ISBN into it's digits.

Is there any elegant solution to this?

Josef 'Jupp' Schugt